INDUCTIVE PROXIMITY SWITCH AND METHOD FOR ITS OPERATION
The invention relates to an inductive proximity switch which has a resonant circuit (Ls, C) comprising a resonant circuit transmission coil (Ls) and a capacitance (C), wherein the resonant circuit transmission coil (Ls) generates an alternating magnetic field which induces a mutual induction voltage in at least one receiving coil (LE), and the oscillation state of the resonant circuit can be influenced by means of a metallic release which enters or moves away from the alternating field. An evaluation circuit is used to obtain a switching signal (uswitch) from the change in the oscillation state of the resonant circuit, wherein the change in the complex coupling between the at least two coils, the transmission coil (Ls) and the receiving coil (LE), can be evaluated, as a switching signal (uswitch), using an auxiliary voltage signal (UHSP) in the presence or absence of the release. The auxiliary voltage signal (UHSP) is obtained in a predefinable ratio (v) as a partial voltage from the resonant circuit voltage (USK) of the resonant circuit (Ls, C), wherein the auxiliary voltage signal (UHSP) is connected in series with the mutual induction voltage induced in the receiving coil (LE) in such a manner that a differential voltage (UD) whose magnitude has been reduced in comparison with the induced mutual induction voltage by the auxiliary voltage signal (UHSP) is obtained at the output of the receiving coil (LE), to earth (G) or to a potential. The differential voltage (UD) is supplied to the evaluation circuit (DG, SK) in a suitable manner in order to obtain the switching signal (Uswitch). The proximity switch may also be in the form of an oscillator.
The invention relates to an inductive proximity switch having a current-fed resonant circuit comprising at least one resonant circuit transmitting coil and a capacitance, the resonant circuit transmitting coil generating an alternating magnetic field, which is able to induct a mutual induction voltage in at least one receiving coil, and the oscillation state of the resonant circuit can be influenced by a metallic release entering or moving away from the alternating field, having an evaluating circuit for obtaining a switching signal from the change in the oscillation state of the resonant circuit, the change in the complex coupling between the at least two coils, namely transmitting coil and receiving coil, being evaluatable with the aid of an auxiliary voltage signal as a switching signal in the presence or absence of the release, according to the preamble of claim 1. The invention also relates to a method for operating such an inductive proximity switch according to the preamble of claim 16.
PRIOR ARTInductive proximity switches are sensors, which react in contactless manner to the approach of a metallic or nonmetallic object or target, i.e. without direct contact. For detecting the approach of such a target by means of an inductive proximity switch, DE-AS 1 286 099 discloses an eddy current method, in which the eddy current losses brought about in an alternating magnetic field by the release are evaluated. For this purpose with a LC resonant circuit an oscillator generates an alternating magnetic field, which changes when eddy current losses occur. As a result there is a change in the oscillation amplitude, which is evaluated by an evaluating circuit on reaching a preset switching value and which is e.g. able to control a relay or some other on-load switch. A disadvantage of such proximity switches is the fact that differently conducting releases lead to differently high eddy current losses and therefore to different response intervals of the proximity switch.
In more recent inductive proximity switches a singe coil is replaced by a transformer having a primary coil and a secondary coil, which are inductively coupled. The magnitude of the coupling between primary and secondary circuit is called the coupling factor which can usually be set between 0 (no coupling) and 1 (perfect coupling), the coupling factor K determining the magnitude of the mutual inductance M of the circuit. A target brought into the switching range of the proximity switch changes the coupling. Coupling evaluation avoids numerous disadvantages associated with proximity switches having only one coil. However, in the prior art it has itself suffered from the disadvantage that it is not easy to implement due to the lower signal level.
In the case of inductive proximity switches with the evaluation of the change of the complex coupling or transimpedance between at least two coils (primary or transmitting coil and secondary or receiving coil, respectively), particularly circuit board coils, in the presence of a metallic target or a metallic release, gives rise to the further following main problems:
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- In particular with increased switching intervals there are extremely low relative changes of the transimpedance (max. a few 1000 ppm/K), which makes a direct secondary voltage evaluation much more difficult.
- The temperature influence on the circuit layout, particularly as a result of the temperature dependence of the real part of the transmitting coil impedance (Cu-losses: Tk=+3800 ppm/K) is considerable.
- When using circuit board coil arrangements and small constructions there are only low transmitting coil impedances and transimpedances, so that correspondingly high currents must flow in order to implement adequately high voltages.
Thus, it is already known from the prior art to implement a current impression in the primary coil and a direct evaluation of the secondary voltage or transimpedance changes, e.g. with a positive feedback amplifier (oscillator). As a result there is an independence from the real part of the transmitting coil impedance. However, this leads to the further problem that small relative changes of the transimpedance require an extreme stability of the amplifier (dv/v max a few 100 ppm/K) and a highly linear power supply. In the case of LP coils, due to the low impedances only low voltage amplitudes are possible, because the possible current amplitude is in practice highly limited.
It is also known to implement a current infeed into a (parallel) resonant circuit formed from the primary coil and a capacitance. This leads to the advantage that the power supply operates against the much higher resonant impedance of the circuit, so that higher amplitudes can be obtained. A disadvantage of this solution is that the resonant impedance or primary voltage, respectively, is highly temperature-dependent (Tk=−3800 ppm/K). As in a good approximation the secondary and primary voltages are proportional, the secondary voltage also has this temperature dependence. Thus, the temperature influences will well cover the useful signal, i.e. the target-induced secondary voltage change.
To boost the relative output signal change it is known from EP 0 479 078 A and U.S. Pat. No. 6,657,323 to subtract a “reference voltage” from the secondary voltage and which is formed by a second secondary coil, which is spatially separated and remains virtually uninfluenced by the release. To this end EP 479 078 A is based on an inductive proximity switch with an oscillator, which feeds a transmitting coil, which generates an alternating magnetic field, the oscillator being influenced in its oscillation state by a metallic release entering the alternating field and with an evaluating circuit for obtaining a switching signal from the oscillation state change. In the alternating field there are two sensor coils in direct differential connection for determining the difference of the voltages induced in both sensor coils, which are so constructed as a result of their spatial position to each other and the number of turns in each case that the alternating differential voltage becomes zero at the desired response interval. The alternating differential voltage is fed back to the input of the oscillator amplifier in such a way that with a zero alternating differential voltage the oscillator suddenly changes its oscillation state. The transmitting coil is connected as an inductance of the LC resonant circuit of the oscillator, the oscillator amplifier input being high-impedance and the two sensor coils with opposite polarisation are connected in series between a voltage divider and the high-impedance input of the oscillator amplifier. This leads to a significantly lower differential voltage which now has a much greater relative change. However, the subtraction by the antiserial interconnection of the two coils leads to the disadvantage that the differential voltage is once again subject to a significant temperature dependence, e.g. Tk=−3800 ppm/K. An intrinsic compensation of the temperature dependence can consequently not be expected. The temperature influence is still reduced in accordance with the increase of the relative change.
DE 19611810A1 discloses a contactless operating proximity switch with a resonant circuit influenceable by metallic objects brought up from the outside and with an evaluating device for obtaining a switching signal from an output signal describing the change of the oscillation state of the resonant circuit. The resonant circuit is a resonant circuit bridge with at least two capacitors and with at least two coils differently influenceable by the objects brought up from the outside, the bridge diagonal voltage being evaluated.
DE 19843749A1 discloses a method for evaluating small changes of a capacitance using an electrical bridge circuit, in whose bridge arms are in each case provided a capacitor in the form of reactances and the bridge is supplied with an alternating voltage as the bridge supply voltage and at least one of the capacitors is variable. The two bridge arm voltages are separately rectified according to the given bridge half, the bridge diagonal voltage only being evaluated following the rectification of the two bridge arm voltages as a direct voltage changing in accordance with the capacitance change.
TECHNICAL PROBLEMThe problem of the invention is to provide an inductive proximity switch, which over a wide temperature range of at least −25° C. to +100° C. has a constant interval with respect to its response behaviour and which can be used as an all-metal switch responding to ferrous and nonferrous metal releases for the same response interval; likewise, it must be possible to use the proximity switch as a selective switch, which responds only to either ferrous or nonferrous metals.
DISCLOSURE OF THE INVENTION AND ITS ADVANTAGES(A1) This problem is solved in the case of an inductive proximity switch of the aforementioned type in that the auxiliary voltage signal is obtained as a partial voltage from the resonant circuit voltage of the resonant circuit in a presettable ratio, the auxiliary voltage signal being connected in series with the mutual induction voltage induced in the receiving coil in such a way that to earth or to a potential a differential voltage is obtained at the output of the receiving coil whose amount is reduced by the auxiliary voltage signal compared with the induced mutual induction voltage, the differential voltage being supplied to the evaluating circuit for obtaining the switching signal.
Thus, on making available an impressed current in the resonant circuit the differential voltage can generally be directly obtained and further processed in an appropriate manner.
(A2) In a further, preferred inventive development of the inductive proximity switch, the latter has a current-fed oscillator comprising at least one resonant circuit transmitting coil and a capacitance, the resonant circuit transmitting coil generating an alternating magnetic field, which is able to induce a mutual induction voltage in at least one receiving coil, and the oscillation state of the oscillator can be influenced by a metallic release entering or moving away from the alternating field, with an evaluating circuit for obtaining a switching signal from the change of the oscillation state of the oscillator, the change in the complex coupling between the at least two coils, namely transmitting coil and receiving coil, being evaluatable with the aid of an auxiliary voltage signal in the form of a switching signal in the presence or absence of the release, the differential voltage, unlike in claim 1, being supplied to a transconductance amplifier for obtaining and feeding back the current proportional to the differential voltage and supplying the oscillator resonant circuit and the resonant circuit voltage is supplied to the evaluating circuit for obtaining the switching signal.
Thus, the inventive inductive proximity switch has the advantage of a virtually perfect temperature independent and at the same time a high relative differential voltage change on approaching a target.
(A3) This can advantageously be obtained in the case of the inventive, inductive proximity switch, no matter whether it is only with a resonant circuit or with an oscillator, in that by means of a presettable ratio between the auxiliary voltage signal and the resonant circuit voltage the differential voltage can be so selected that the said differential voltage becomes temperature-independent either in the case of resonance of the resonant circuit or in the resonance amplitude of the resonant circuit voltage, respectively, or is temperature-independent for a resonant circuit voltage amplitude which is located symmetrically to the resonant frequency of the resonant circuit on the resonance slopes.
(A15) In a further advantageous development of such an inventive proximity switch, by means of a power source a supply current is impressed on the resonant circuit and the differential voltage is supplied to an amplifier, to whose output is connected one input of a multiplier, and to whose other input is applied the phase information of the current supplying the resonant circuit, preferably being influenced by means of a phase shifter, the multiplier output being supplied to the evaluating circuit for obtaining the switching signal.
Said temperature independence is obtained both in the case of a resonant circuit with an impressed supply current and in particular with an oscillator with a fed-back supply current.
(A4) In a further advantageous development of the inventive proximity switch, in which the resonant circuit is connected to an oscillator, the transconductance amplifier has a selectable slope.
(A5) In an advantageous development of the inventive inductive proximity switch for obtaining the auxiliary voltage signal as a partial voltage in a presettable ratio from the resonant circuit voltage of the resonant circuit, the resonant circuit voltage is applied to the inputs of an amplifier with presettable gain, whose output signal, either to earth or to a potential, forms the auxiliary voltage signal, one end of the receiving coil being applied to the amplifier output and, to earth or to a potential, the differential voltage is obtained at its other end.
(A6) In a further advantageous development of the proximity switch for obtaining the auxiliary voltage signal as a partial voltage in a presettable ratio from the resonant circuit voltage of the resonant circuit, a complex voltage divider from a series connection of two complex resistors is connected in parallel thereto, the auxiliary voltage signal falling across the second complex resistor and one end of the receiving coil is applied to the centre point of the voltage divider and the differential voltage is obtained at its other end.
Thus, the complex voltage divider with at least the complex resistors Z1 and Z2 divides the circuit or primary voltage in an adjustable ratio v, so that through the corresponding choice of the divider ratio
v=Z2/(Z1+Z2)
a differential voltage uD to earth or ground is obtained, which has both a virtually perfect temperature independence and also a high relative change on approaching the target. As a result a self-compensated system can be obtained. Moreover, in highly advantageous manner, no second, remote secondary coil is needed.
(A7) In a further advantageous development of the proximity switch the series connection of the two complex resistors of the voltage divider is a series connection of two capacitors, the auxiliary voltage signal falling across the second of the two capacitors.
(A8) It is possible for the capacitance of the resonant circuit to be wholly or partially formed by the capacitors or one of the capacitors or the self-capacitance of the transmitting coil.
The use of the aforementioned network designs with an amplifier or a preferably complex voltage divider are also independent of whether use is made of a resonant circuit with an impressed supply current or an oscillator with a fed-back supply current.
(A9) In a further development of the inventive proximity switch for obtaining the auxiliary voltage signal as a partial voltage in a presettable ratio from the resonant circuit voltage of the resonant circuit, with the latter is connected in parallel a complex voltage divider of a series connection of two complex resistors, the auxiliary voltage signal falling across the second complex resistor and is simultaneously applied to two signal inputs of an impedance converter and one end of the receiving coil is applied to the output of the impedance converter and the differential voltage is obtained at the output of the receiving coil, to earth or to a potential. Thus, the centre tap of the voltage divider is applied to one input of the impedance converter, to whose other input is applied the joint base of the resonant circuit and voltage divider, i.e. in the simplest case to earth or ground, the auxiliary voltage being supplied by the impedance converter output signal.
(A10) In a further development of the proximity switch at least one of the two complex resistors of the complex voltage divider is adjustable, so that the resonant circuit voltage of the resonant circuit is divided in an adjustable ratio and consequently an adjustable differential voltage is obtained at the receiving coil output.
(A11) Moreover, the voltage divider of the inventive proximity switch can be implemented with ohmic resistors.
(A12) In a further development of the proximity switch the transmitting coil and receiving coil form a planar coil system. (A13) In the same way the transmitting coil and receiving coil can be implemented as circuit board coils.
(A14) In a further development of the proximity switch the resonant circuit voltage is rectified and supplied to a threshold discriminator for obtaining the switching signal.
(A16) Furthermore, the auxiliary or differential voltage uHsp through a correspondingly positioned tap can be obtained by a tapping point at the transmitting coil LS, said tapping point subdividing the transmitting coil LS into the partial inductances LS1, and LS2.
(A17) The voltage obtained from the coil tap of transmitting coil LS can be amplified in an amplifier A or impedance converter, respectively, so that the auxiliary or differential voltage uHsp, respectively, is available downstream of the amplifier.
(A18) From the method standpoint the set problem for the operation of an inductive proximity switch of the aforementioned type is solved in that the auxiliary voltage signal is obtained as a partial voltage from the resonant circuit voltage of the resonant circuit in a presettable ratio, the auxiliary voltage signal being so connected in series with the mutual induction voltage induced in the receiving coil that at the output of said receiving coil, to earth or to a potential, a differential voltage is obtained, whose quantity is reduced by the auxiliary voltage signal compared with the induced mutual induction voltage, the differential voltage being supplied to the evaluating circuit for obtaining the switching signal.
(A19) In a further advantageous development of the inventive method and when using an oscillator with fed-back current infeed, the differential voltage is supplied to a trans-conductance amplifier, whose current proportional to the differential voltage is fed back into the oscillator resonant circuit, the resonant circuit voltage being supplied to the evaluating circuit for obtaining the switching signal.
(A20) From the method standpoint it is possible in this way to divide the resonant circuit voltage of the resonant circuit in an adjustable ratio and consequently obtain at the receiving coil output an adjustable differential voltage.
(A21) In a further inventive development of the method, by means of the presettable ratio between auxiliary voltage signal and resonant circuit voltage, the differential voltage is so selected that it becomes temperature-independent either at resonance of the resonant circuit or in the resonance amplitude of the resonant circuit voltage, respectively, or becomes temperature-independent for an amplitude of the resonant circuit voltage, which is located symmetrically to the resonant frequency of the resonant circuit on the resonance slopes.
(A22) Generally the invention is consequently characterized by a network for the operation of an inductive proximity switch, the network having a current-fed resonant circuit comprising at least one resonant circuit transmitting coil and a capacitance, and the resonant circuit transmitting coil generates an alternating magnetic field, which is able to induce a mutual induction voltage in at least one receiving coil, and the oscillation state of the resonant circuit can be influenced by a metallic release entering or moving away from the alternating field, and from the change of the oscillation state of the resonant circuit it is possible to obtain a switching signal, the change to the complex coupling between the at least two coils, namely transmitting coil and receiving coil, being evaluatable as a switching signal with the aid of an auxiliary voltage signal in the presence or absence of the release. The auxiliary voltage signal is obtained as a partial voltage from the resonant circuit voltage of the resonant circuit of the network in a presettable ratio, the auxiliary voltage signal being connected in series with the mutual induction voltage induced in the receiving coil in such a way that, to earth or to a potential, a differential voltage is obtained at the receiving coil output, the amount of which is reduced by the auxiliary voltage signal compared with the induced mutual induction voltage, the switching signal being generated from the differential voltage.
Within the dotted line guide of
To obtain an auxiliary voltage signal uHsp as a partial voltage from the resonant circuit voltage uSK of the resonant circuit LS, C application takes place parallel to the latter of a complex voltage divider comprising the two complex resistors Z1 and Z2, the voltage falling across the second-mentioned complex resistor Z2 of the voltage divider being the auxiliary voltage uHsp or the auxiliary voltage signal uHsp. One end of the receiving coil LE is supplied to the centre point M between the two complex resistors Z1 and Z2, so that the auxiliary voltage signal uHsp is subtracted from or added to, respectively, the mutual induction voltage induced in receiving coil LE and thus the aforementioned, induced differential voltage uD is obtained at the output of receiving coil LE, either to earth or ground G or to a potential and the amount thereof is reduced by the auxiliary voltage signal uHsp compared with the mutual induction voltage induced in receiving coil LE. As will be described in greater detail relative to
Preferably the impedance of the voltage tap of differential voltage uD is higher than Z2. From the circuit is obtained a divider ratio v for the complex voltage divider of:
v=Z2/(Z1+Z2).
A more general circuit for implementing the invention is explained relative to network T of
Within the network T,
v=C1/(C1+C2).
The auxiliary voltage uHsp or auxiliary voltage signal uHsp falls across the capacitor C2, which in
The differential signal uD is obtained at the output of receiving coil LE. The special point here is that the capacitance of the resonant circuit can be included in the capacitance C1 or the capacitances C1+C2, so that the resonant circuit can be formed from transmitting coil LS and one of or the series connection of the capacitances C1, C2.
For the generation of the auxiliary voltage signal uHsp, network T of
The divider ratio v is here formed by:
v=R2/(R1+R2).
The above-described networks T of
In
In
k=0.2588->M=546 nH
RS=2.7 Ohm (@ 25° C.), a=3800 ppm/K (Cu)
C1=1.5 nF, C2=variable; i1=1 mA.
When e.g. using the aforementioned values of the circuit components in an inductive proximity switch in accordance with the circuit of
Examples 1 and 2 in
The respective capacitor C2, across which the auxiliary voltage signal uHsp falls, has a size C2=7.65 nF or 7.30 nF, respectively, which gives v=C1/(C1+C2)=0.164 and 0.170 respectively. On the ordinate is plotted the resonant circuit voltage uSK/V and on the abscissa the resonant circuit frequency f/MHz. It is clear that on operating the resonant circuit at different temperatures (−25° C., 25° C., 75° C.), at which naturally different resonance amplitudes are obtained, the associated differential voltage signals uD have a substantially identical amplitude maximum.
The same applies according to
In the embodiments of
The invention can in particular be commercially used in inductive proximity switches in order to significantly improve the temperature independence and relative change during the approach of a target or a release with a more or less good conducting characteristic.
REFERENCE NUMERALS LISTLS Transmitting coil
LE Receiving coil
C Resonant circuit capacitance
Z1, Z2 Complex resistors of a voltage divider
C1, C2 Capacitors of a capacitive voltage divider
R1, R2 Ohmic resistors of a voltage divider
uHsp Auxiliary voltage or auxiliary voltage signal
uD Differential voltage or differential voltage signal
G Earth or ground
IW Impedance converter
m Amplifier gain
S Transconductance amplifier
DG Diode rectifier
SK Threshold discriminator
uswitch Voltage switching signal of evaluating circuit
uSK Resonant circuit voltage
LS, C Resonant circuit
is Supply current for the resonant circuit
PS Phase shifter
pi Phase information from supply current is
IS Power source
Claims
1. Inductive proximity switch having a current-fed resonant circuit (LS, C), comprising at least one resonant circuit transmitting coil (LS) and a capacitor (C), the resonant circuit transmitting coil (LS) generating an alternating magnetic field, which is able to induce a mutual induction voltage in at least one receiving coil (LE), and the oscillation state of the resonant circuit can be influenced by a metallic release entering or moving away from the alternating field, with an evaluating circuit for obtaining a switching signal (uswitch) from the change of the oscillation state of the resonant circuit, the change of the complex coupling between the at least two coils, namely transmitting coil (LS) and receiving coil (LE), being evaluatable as a switching signal (uswitch) with the aid of an auxiliary voltage signal (uHsp) in the presence or absence of the release,
- characterized in that
- the auxiliary voltage signal (uHsp) is obtained as a partial voltage from the resonant circuit voltage (uSK) of the resonant circuit (LS, C) in a presettable ratio (v), the auxiliary voltage signal (uHsp) being so connected in series with the mutual induction voltage induced in receiving coil (LE) that, to ground (G) or to a potential, a differential voltage (uD) is obtained at the output of receiving coil (LE) and whose amount is reduced by the auxiliary voltage signal (uHsp) compared with the induced mutual induction voltage, the differential voltage (uD) being supplied to the evaluating circuit (SK) for obtaining the switching signal (uswitch).
2. Inductive proximity switch having a current-fed oscillator comprising at least one resonant circuit transmitting coil (LS) and a capacitance (C), the resonant circuit transmitting coil (LS) generating an alternating magnetic field, which is able to induce a mutual induction voltage in at least one receiving coil (LE) and the oscillation state of the oscillator can be influenced by a metallic release entering or moving away from the alternating field, with an evaluating circuit for obtaining a switching signal (uswitch) from the change of the oscillation state of the oscillator, the change of the complex coupling between the at least two coils, namely transmitting coil (LS) and receiving coil (LE), being evaluatable as a switching signal (uswitch) with the aid of an auxiliary voltage signal (uHsp) in the presence or absence of the release according to claim 1,
- characterized in that,
- unlike in claim 1, the differential voltage (uD) is supplied to a transconductance amplifier (TK) for obtaining and returning the current (i1) proportional to the differential voltage (uD) and feeding the resonant circuit (LS, C) of the oscillator and the resonant circuit voltage (uSK) is supplied to the evaluating circuit (DG, SK) for obtaining the switching signal (uswitch).
3. Inductive proximity switch according to claim 1 or 2,
- characterized in that
- by means of the presettable ratio (v) between auxiliary voltage signal (uHsp) and resonant circuit voltage (uSK) the differential voltage (uD) can be so selected that the differential voltage (uD) becomes temperature-independent either at resonance of the resonant circuit (LS, C) or in the resonance amplitude of the resonant circuit voltage (uSK), respectively, or is temperature-independent for an amplitude of the resonant circuit voltage (uSK) which is symmetrically located to the resonant frequency of the resonant circuit (LS, C) on the resonance slopes.
4. Inductive proximity switch according to one of the preceding claims,
- characterized in that
- the transconductance amplifier (TK) has a selectable slope (s).
5. Inductive proximity switch according to one of the claims 1 to 4,
- characterized in that
- for obtaining the auxiliary voltage signal (uHsp) as a partial voltage in a presettable ratio (v) from the resonant circuit voltage (uSK) of the resonant circuit (LS, C) the resonant circuit voltage is applied to the inputs of an amplifier (V) with presettable gain (m), whose output signal, either to ground (G) or to a potential, forms the auxiliary voltage signal (uHsp) and to the output of amplifier (V) is applied the one end of the receiving coil (LE) and at its other end, to ground (G) or to a potential, is obtained the differential voltage (uD).
6. Inductive proximity switch according to one of the claims 1 to 4,
- characterized in that
- for obtaining the auxiliary voltage signal (uHsp) as a partial voltage in a presettable ratio (v) from the resonant circuit voltage (uSK) of the resonant circuit (LS, C) a complex voltage divider resulting from a series connection of two complex resistors (Z1, Z2) is connected in parallel thereto and the auxiliary voltage signal (uHsp) falls across the second complex resistor (Z2) and to the centre point (M) of voltage divider (Z1, Z2) is applied the one end of receiving coil (LE) and at whose other end is obtained the differential voltage (uD).
7. Inductive proximity switch according to claim 6,
- characterized in that
- the series connection of the two complex resistors of the voltage divider is a series connection of two capacitors (C1, C2) and the auxiliary voltage signal (uHsp) falls across the second (C2) of the two capacitors (C1, C2).
8. Inductive proximity switch according to claim 7,
- characterized in that
- the capacitance (C) of the resonant circuit is wholly or partially formed by the capacitors (C1, C2) or one of the capacitors (C1, C2) or the self-capacitance of transmitting coil (LS).
9. Inductive proximity switch according to one of the claims 1 to 4,
- characterized in that
- for obtaining the auxiliary voltage signal (uHsp) as a partial voltage in a presettable ratio (v) from the resonant circuit voltage (uSK) of the resonant circuit (LS, C), a complex voltage divider resulting from a series connection of two complex resistors (Z1, Z2) is connected in parallel therewith and the auxiliary voltage signal (uHsp) falls across the second (Z2) complex resistor (Z1, Z2) and simultaneously an impedance converter (IW) is applied to the two signal inputs, the one end of the receiving coil (LE) being applied to the output of impedance converter (IW) and, to ground (G) or to a potential, the differential voltage (uD) is obtained at the output of receiving coil (LE).
10. Inductive proximity switch according to one of the claims 6 to 9,
- characterized in that
- at least one of the two complex resistors (Z1, Z2) of the complex voltage divider is adjustable, so that the resonant circuit voltage (uSK) of the resonant circuit (LS, C) is divided in an adjustable ratio (v) and consequently an adjustable differential voltage (uD) is obtained at the output of receiving coil (LE).
11. Inductive proximity switch according to one of the claims 6 to 10,
- characterized in that
- the voltage divider is implemented with ohmic resistors (R1, R2).
12. Inductive proximity switch according to one of the preceding claims,
- characterized in that
- the at least one transmitting coil (LS) and the at least one receiving coil (LE) form a planar coil system.
13. Inductive proximity switch according to one of the preceding claims,
- characterized in that
- the at least one transmitting coil (LS) and the at least one receiving coil (LE) are in the form of circuit board coils.
14. Inductive proximity switch according to one of the preceding claims,
- characterized in that
- the resonant circuit voltage (uSK) is rectified and supplied to a threshold discriminator (Sk) for obtaining the switching signal (uswitch).
15. Inductive proximity switch according to claim 1,
- characterized in that
- by means of the power source (IS) a supply current (i1) is impressed on the resonant circuit and the differential voltage (uD) is supplied to an amplifier (V2), to whose output is connected the one input of a multiplier (MP) and to whose other input is applied the phase information (pi) of the supply current (i1), preferably influenced by means of a phase shifter, and the output of multiplier (MP) is supplied to the evaluating circuit (DG, Sk) for obtaining the switching signal (uswitch).
16. Inductive proximity switch according to one of the claims 1 or 2,
- characterized in that
- the auxiliary or differential voltage (uHsp), respectively, is obtained by a correspondingly positioned tap through a tapping point on the transmitting coil (LS), said tapping point subdividing transmitting coil (LS) into the partial inductances (LS1) and (LS2).
17. Inductive proximity switch according to claim 16,
- characterized in that
- the voltage obtained from the coil tap of transmitting coil (LS) is amplified in an amplifier (A) and the auxiliary or differential voltage (uHsp), respectively, is available downstream of the amplifier.
18. Method for operating an inductive proximity switch, with a resonant circuit (LS, C) comprising at least one resonant circuit transmitting coil (LS) and a capacitance (C), the resonant circuit transmitting coil (LS) generating an alternating magnetic field, which induces a mutual induction voltage in at least one receiving coil (LE) and the oscillation state of the resonant circuit is influenced by a metallic release entering or moving away from the alternating field, with an evaluating circuit for obtaining a switching signal (uswitch) from the change of the oscillation state of the resonant circuit, the change of the complex coupling between the at least two coils, namely transmitting coil (LS) and receiving coil (LE), being evaluated as a switching signal (uswitch) with the aid of an auxiliary voltage signal (uHsp) in the presence or absence of the release,
- characterized in that
- the auxiliary voltage signal (uHsp) is obtained as a partial voltage from the resonant circuit voltage (uSK) of the resonant circuit (LS, C) in a presettable ratio (v), the auxiliary voltage signal (uHsp) being so connected in series with the mutual induction voltage induced in the receiving coil (LE) that at the output of the receiving coil (LE) a differential voltage (uD) is obtained to ground (G) or to a potential and whose amount is reduced by the auxiliary voltage signal (uHsp) compared with the induced mutual induction voltage, the differential voltage (uD) being supplied to the evaluating circuit (DG, SK) for obtaining the switching signal (uswitch).
19. Method for operating an inductive proximity switch, which has an oscillator comprising at least one resonant circuit transmitting coil (LS) and a capacitance (C), the resonant circuit transmitting coil (LS) generating an alternating magnetic field, which induces a mutual induction voltage in at least one receiving coil (LE), and the oscillation state of the oscillator can be influenced by a metallic release entering or moving away from the alternating field, with an evaluating circuit for obtaining a switching signal (uswitch) from the change of the oscillation state of the oscillator, the change of the complex coupling between the at least two coils, namely transmitting coil (LS) and receiving coil (LE), being evaluated as a switching signal (uswitch) with the aid of an auxiliary voltage signal (uHsp) in the presence or absence of the release, according to claim 1,
- characterized in that
- the differential voltage (uD) is supplied to a transconductance amplifier (TK), whose current (i1) proportional to the differential voltage (uD) is fed back into the resonant circuit (LS, C) of the oscillator, and the resonant circuit voltage (uSK) is supplied to the evaluating circuit (DG, SK) for obtaining the switching signal (uswitch).
20. Method according to claim 18 or 19,
- characterized in that
- the resonant circuit voltage (uSK) of the resonant circuit (LS, C) is divided in an adjustable ratio (v) and as a result an adjustable differential voltage (uD) is obtained at the output of the receiving coil (LE).
21. Method according to one of the claims 18 or 19,
- characterized in that
- by means of the presettable ratio (v) between the auxiliary voltage signal (uHsp) and the resonant circuit voltage (uSK), the differential voltage (uD) is so selected that the differential voltage (uD) either becomes temperature-independent at resonance of the resonant circuit (LS, C) or in the resonance amplitude of the resonant circuit voltage (uSK), respectively, or becomes temperature-independent for an amplitude of the resonant circuit voltage (uSK) which is located symmetrically to the resonant frequency of the resonant circuit (LS, C) on the resonance slopes.
22. Network for the operation of an inductive proximity switch, the network having a current-fed resonant circuit (LS, C) comprising at least one resonant circuit transmitting coil (LS) and a capacitance (C), and the resonant circuit transmitting coil (LS) generates an alternating magnetic field, which is able to induce a mutual induction voltage in at least one receiving coil (LE), and the oscillation state of the resonant circuit can be influenced by a metallic release entering or moving away from the alternating field, and from the change of the oscillation state of the resonant circuit can be obtained a switching signal (uswitch), the change of the complex coupling between the at least two coils, namely transmitting coil (LS) and receiving coil (LE), being evaluatable as a switching signal (uswitch) with the aid of an auxiliary voltage (uHsp) in the presence or absence of the release,
- characterized in that
- the auxiliary voltage signal (uHsp) is obtained as a partial voltage from the resonant circuit voltage (uSK) of the resonant circuit (LS, C) of the network in a presettable ratio (v), the auxiliary voltage signal (uHsp) being so connected in series with the mutual induction voltage induced in the receiving coil (LE) that at the output of the receiving coil (LE), to ground (G) or to a potential, is obtained a differential voltage (uD), whose amount is reduced by the auxiliary voltage signal (uHsp) compared with the induced mutual induction voltage, the switching signal (uswitch) being generated from the differential voltage (uD).
Type: Application
Filed: Feb 21, 2007
Publication Date: Oct 1, 2009
Patent Grant number: 9479165
Inventor: Thomas Kuehn (Mannheim)
Application Number: 12/280,048
International Classification: G01V 3/10 (20060101);